TB risk for newborn - how high?

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DD2 should have been given her bcg at birth but the hospital forgot. No problem said the HV, ring this number and get it done at this hospital. We live in london and our postcode (N4) is considered high risk so I was shocked to be told the first appointment wasn't until December.
Now the HV says dd's risk is very low and it's nothing to worry about and not worth forking out £70 to go private.
But if she's not high risk why do they give it at birth at all? I trust the HV is giving me her honest opinion but to me, it doesn't add up that one minute my baby is so high risk she needs a jab at birth and the next she's fine to wait four months.
Does anyone have any expertise in this matter and can advise on dd2's risk?
I wanted to go to town today but was reluctant to take her on tube before she has her bcg.

they determine risk by things like:
ethnicity as well as postcode.

i was offered it as i was born overseas and that my dd is more likely to travel to 'high risk' places and more likely to come into tb infected individuals for long periods of time than 'white folks' are.

i giggled to myself because the country where i am likely to take her for a long time has a v. low tb prevalence.

If I remember right, TB jabs aren't given as a matter of routine any more. They're only given to 'high risk' communities, often those in places where there are a lot of people from parts of the world with endemic TB. If no-one in your immediate family or people your dd is likely to come into close and prolonged contact with (live with, be cared for by) are from a high risk group then her risk will not be high. Postcodes are just a convenient way of getting to a decent proportion of the people who should be immunised. As is immunisation at birth (ie when someone is in the system and less likely to slip through the net). What that all adds up to is, I really don't think you have much to worry about. Have a look at this page.

thanks for replies. i take the point about 'prolonged'contact being substantial and repeated amounts of time but wasn't there a fuss a while ago about it being spread by air in planes? And no, i don't expect to be on the tube for anything like that amount of time... I'm just trying to weigh this up.
DH agrees with health visitor.
Has motherhood turned me neurotic?
I never used to worry about things this much but now all i can think is i'd never forgive myself if she got sick cos i didn't pay for a jab.

My DD's weren't given the bcg at birth and I had them at the whittington which is your nearest hospital. I lived in N4 for most of my pregnancy and it was never mentioned to me during any of my appointments.

oh really? that makes me feel a bit better, thanks goingfor3.
maybe i should relax..!

i live in n4 and my girls had bcg at 6 weeks. we also recently had a questionnaire about it from school (an islington school) so assume they catch those who didn't have it before.

Selfishly, this is good for me (I am supposed to be doing infectious diseases revision for an exam not messing on mumsnet!). So I've just looked up TB, and this is what my textbook says:

"How to assess the likelihood of transmission of TB

1. How infectious is the source case? (there's not much point in going into this as you have no way of knowing)
2. How great is the exposure? Exposure to coughing is the most important risk. Prolonged multiple indoor exposure usually needed to affect most contacts. Risk highest in household and close associates of case. Brief contact = low risk. Outdoor contact = very low risk.
3. how susceptible is the contact to infection? Susceptibility varies by age. neonates = very high. Under 3 = high."

Soooo, if you are worried, and likely to be on the tube for a long time and think that your fellow passengers may be TB+ve and cough directly over your daughter, then don't travel on closed transport like that until after BCG (which btw is not that great a jab and reduces risk by 50-80%), or until she is older. But as I understand it, to become infected you need to be sprayed with TB infected droplets from someone who is sputum +ve, and breath the droplets in - may be a good excuse to stop people coming too close if you don't like that sort of thing.

is that any help?

thanks greenglassgoblin, that is very useful and has allowed me to relax about tb and spend today stressing about colic !
Good luck with your revision and thanks again.